In order to perform an operation, lubrication, cooling, or the like of an automatic transmission or the like mounted on a vehicle, in general, oil supply (oil-pressure supply) is performed using a hydraulic pump (mechanical oil pump) driven by an internal combustion engine (engine) which is a drive source mounted on the vehicle. The mechanical oil pump is connected to an engine, and specifications (natural discharging amount) of the pump are determined from a maximum flow rate and an engine speed required for a transmission, and are associated with the rotating speed of an engine.
Accordingly, when an idle reduction function or the like is provided on an engine, if the engine is automatically stopped, the mechanical oil pump is also stopped. As a result, the transmission may be in a neutral state or supply of oil to a clutch may be stopped due to a decrease in an oil pressure according to a kind of the engine.
If the transmission enters a neutral state, engagement of the transmission is generated when the oil pressure is increased by actuation of the engine, and vibration occurs due to a difference of rotating speeds. In addition, there may be a problem that if supply of oil for lubricating and cooling to the clutch is stopped, cooling of the clutch may be not sufficient, and the clutch may be heated.
Accordingly, there is a method in which an electric oil pump which is able to be operated independently of an engine is provided in parallel with a mechanical oil pump, oil supply (oil-pressure supply) is performed on a required portion by the electric oil pump during stopping of the engine, a predetermined oil pressure is secured even during stopping of the engine, and a state of each portion is maintained (for example, refer to Patent Document 1).
In addition, in a hybrid electric vehicle (HEV), a method is known, in which a hydraulic pump is able to be driven by both an engine and a traveling motor, and the hydraulic pump is able to be driven by input from both the engine and the traveling motor (refer to Patent Document 2,, Patent Document 3,, or the like).
In addition, in Patent Document 2,, an electric oil pump which is driven by a dedicated motor is provided in addition to a mechanical oil pump which is driven by the engine and the traveling motor, and the electric oil pump compensates for a lack in the amount of discharge in a region in which a rotating speed of the mechanical oil pump decreases.